To the question, “why do cats purr”, the answer seems obvious because we have all heard a cat purr when he or she is content. You stroke a cat and it purrs. Your cat jumps up and kneads your lap and purrs. Surely the reason for the purr is to show contentment. This, though, is not correct. Some of us have heard a cat purr when in pain but perhaps we didn’t recognise that moment. Or say in a vets about to euthanized and your cat purrs. These are not content cats. So what is the underlying process that causes a cat to purr? In other words what is a common factor in what appears to be almost opposite situations and emotions? Can there be a common factor? Yes, is the answer.
A cat likes to make a place its own by leaving scent on it. It does this by spraying urine to tell others that this area is its home range. It makes us more friendly by rubbing against us. This leaves us smelling friendly to the cat. It purrs for similar reasons, which is to communicate a need for friendship (in the case of being in pain for example) and/or to communicate a thank you for friendship received (in the case of being stroked for example).
This form of communication relates to adult cats. It is a secondary purpose for the act of purring and an extension of the primary purpose when it is used as a kitten.
The first time a cat purrs is when it is receiving its mother’s milk. The kitten is signalling to its mother that is is receiving milk and all is well; while the mother might purr back to signal the same. At that moment, the process of nursing her cats is in order and the mother is reassured.
Purring can take place while the mouth is closed and while drinking the mother’s milk. It happens when air passes in both directions – when inhaling and exhaling. I discuss the actual mechanism in outline on this page: How Do Cats Purr?
Most wild cats purr too. You can hear a puma (cougar or mountain lion) purr on this page: Cat Sounds WAV WMA MP3. However the big cats cannot purr. The big cats are the:
These cats can roar though. But the reason for roaring is not the same as for purring. The tiger roar is a loud sound that is said to travel up to 5 miles. Its purpose is obviously long distance communication. It is sometimes made as a prelude to mating with a tigress or after killing a large animal.